1. Field of the Invention
The present invention relates generally to a fuel volume measuring system for an automotive vehicle and more specifically to a fuel volume measuring system for digitally indicating the amount of fuel in a fuel tank installed on an automotive vehicle, even when the vehicle is running or is being refueled; in other words, when the fuel level within the fuel tank surges or undulates or is stationary.
2. Description of the Prior Art
Conventionally, an analog fuel volume measuring apparatus is widely used for an automotive vehicle. The analog fuel volume measuring apparatus usually includes a float moved up and down according to the fuel level within a fuel tank, a resistor-type potentiometer actuated in relation to the upward-and-downward movement of the float, a DC amplifier for amplifying the output voltage signal of the potentiometer, and a meter having a pointer pivoted clockwise to indicate a fuel volume by means of an electromagnetic transducer in accordance with the magnitude of the signal outputted from the DC amplifier.
On the other hand, recently, a digital fuel volume measuring system has come into use for an automotive vehicle. The digital fuel volume measuring system can indicate the amount of fuel within a fuel tank digitally and precisely in the unit of 1.0 or 0.1 liter, for instance. In such a digital system as described above, on the basis of the accurate digital data indicative of the fuel volume within a fuel tank, it is also possible to obtain other useful information necessary for the driver or the user.
In such a digital fuel volume measuring system for an automotive vehicle, however, when the vehicle is running and thereby the fuel level within the fuel tank surges, there exist the following disadvantages: In the case where an automotive vehicle turns, starts, stops, is accelerated or decelerated, goes up a slope, reaches the head of a slope, starts going down a slope, and reaches the foot of a slope, a great acceleration is inevitably applied to a fuel tank for the vehicle and therefore the fuel within the fuel tank surges, thus causing the fluctuations of the fuel level and therefore the fluctuations of digital indication of fuel volume.
In the case of the analog fuel measuring apparatus of pointer type, even if the fuel level fluctuates within the fuel tank, these fluctuations do not give rise to a serious problem. This is because the response speed of the pointer itself is not high because of the structure thereof. Therefore, even if the signal indicative of fuel volume varies, the pointer does not oscillate, and further even if the pointer oscillates violently, no special sense of disorder with respect to the indication is given to the driver.
In contrast with this, in the case of a digital fuel volume measuring system, when the signal indicative of fuel volume fluctuates, the indicated numerical value changes or flickers and a sense of disorder with respect to the indication is given to the driver, thus eventually resulting in a danger such that the user has some doubts about the reliability of the fuel indication.
For the reason as described above, there has been proposed a fuel volume measuring system for an automotive vehicle which can suppress the fluctuations of measured fuel volume in dependence upon the method of simply averaging the data signals indicative of fuel volume. In such a prior-art fuel volume measuring system for an automotive vehicle, however, since the fuel volume is calculated on the basis of the simple averaging method, the time interval during which the data signals indicative of fuel volume are averaged is inevitably increased in order to sufficiently suppress the fluctuations of fuel volume, with the result that the time interval from when the current fuel volume is indicated to when the succeeding fuel volume is indicated is prolonged; that is, the response characteristic in measuring the fuel volume is unsatisfactory. Further, when the time interval during which the fuel volume data signals are averaged is decreased in order to improve the response characteristic, it is impossible to sufficiently suppress the fluctuations of fuel volume indication. To explain the prior-art fuel volume measuring system on the basis of experimental numerical values, in the case where the time interval during which fuel volume data signals are averaged is predetermined to be from 1 to 2 minutes, the fuel volume indication fluctuates 1 to 2 liters.
On the other hand, in such a fuel volume measuring system as described above, since the averaging time interval or the response characteristic is appropriately determined only in the state where the vehicle is running, there exists another problem in that, when the vehicle is being refueled, that is, when the fuel volume increases abruptly in a short time period, the fuel volume is not indicated immediately at a high response speed to the driver but indicated one or two minutes later.
Additionally, in such a fuel volume measuring system as described above, since the averaging time interval or the response characteristic is inevitably long, there exists another problem in that, when the vehicle is started with the ignition key inserted into the key hole, the fuel volume is not immediated indicated to the driver but indicated one or two minutes later.
Therefore, it is necessary to detect whether the vehicle is running or kept stopped, in order to change the averaging time interval according to the vehicle running condition. In more detail, when the vehicle is running, the averaging time interval is determined to be long to sufficiently suppress the fluctuations of fuel volume indication and therefore the response time of fuel volume indication is long; when the vehicle is being refueled or is stationary the averaging time interval is determined to be short to improve the response time of fuel volume indication and therefore the fluctuations of fuel volume indication are not suppressed when the fuel surges.
In the prior-art fuel volume measuring system, however, the vehicle running condition is usually detected in dependence upon the positions of the ignition key. Therefore, when the ignition switch is once set to the OFF position during refueling and then set to the ON position again in order to confirm the fuel volume when or after the vehicle is refueled, since the averaging time interval is already set to a long time interval during which fuel volume data signals are averaged, in spite of the fact that the vehicle is being refueled or has been refueled completely, the fuel volume is not immediately indicated to the driver. On the other hand, in the case where a vehicle speed sensor is used for detecting the vehicle running condition, when the vehicle is running at a very slow speed on a busy road, for instance, since the sensor detects that vehicle speed is zero and therefore the sensor determines that the vehicle is being refueled, the averaging time interval is already set to a short time interval during which fuel volume data signals are averaged, in spite of the fact that the vehicle is running, the digital fuel volume indication fluctuates or flickers without accurately indicating the fuel volume.
In brief summary, in the prior-art fuel volume measuring system for an automotive vehicle, since the data signals indicative of fuel volume are simply averaged in order to suppress the fluctuations of the fuel volume, and therefore the averaging time interval is relatively long, it has been impossible to improve the response characteristic of fuel volume indication. Additionally, since the vehicle running condition is simply detected in dependence upon the ignition key position or by means of a vehicle sensor, it has been impossible to securely detect that the vehicle is running or being refueled.
The system configuration of the prior art fuel volume measuring system for an automotive vehicle will be described in more detail hereinafter with reference to the attached drawing under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.